Automatic label dispensers are being used more and more. One area of use is in supermarkets where prices are imprinted on a label and applied to the merchandise by an automatic hand held labelling machine. One machine of this type is described in U.S. Pat. No. 4,264,396 issued to Stewart. In this machine, labels releasably adhered to a support strip are stored in a cassette from which they are dispensed to a thermal printer as needed. Dot indicia are placed on the support strip between each label to be detected by a photocell and thereby control the incremental advance of each label to the printer.
Unfortunately, if the dot formed on the substrate between each label is not of uniform density or if there are skips, the positioning of each label may not always be positively achieved. Also, if the cassette is not placed securely in its receptacle in the printer mechanism, the labels can become somewhat skewed, again creating problems. In extreme cases, the skewing, because of an improperly seated cassette, can cause the label advance to jam.
The label dispensing system described in U.S. Pat. No. 3,997,384, which senses the differences in reflectivity between a label and the label substrate, suffers from similar disadvantages.
In another label printing system, such as that described in U.S. Pat. No. 4,048,494, the label advance is controlled by passing a light beam directly through a transparent substrate. In this manner the proper advance of each label to the print area is controlled. This system suffers from many of the same disadvantages as those discussed above. If the cassette is not in the proper position the support strip can become skewed causing undue friction. Also, if the optical density of the support strip varies or becomes marked, a false label detection can occur.